The International Space Station is now two tons heavier, with the installation today of its newest truss segment during the flight’s first spacewalk.

Mission Specialists Bob Curbeam and Christer Fuglesang ventured outside the station to attach the P5 segment of the station’s truss and replace a failed camera needed to support future assembly tasks. They also were able to fit in some extra tasks that will save future spacewalkers time, including plugging the new segment into the existing truss, removing the locks that held it steady during launch and opening a latch that will allow the P6 segment to be attached when it is moved from its current, temporary location to its permanent place at the end of the port truss.

The spacewalk began at 2:31 p.m. CST, and Curbeam and Fuglesang were back inside by 9:07 p.m. The truss was officially attached at 4:45 p.m., and installation was complete by 5:21 p.m. Total duration of the spacewalk was 6 hours, 36 minutes.

Upon their return to the Quest airlock at the end of the spacewalk, Curbeam took a moment to congratulate Nobel Prize winners, including Dr. John C. Mather, a Goddard Space Flight Center scientist honored for his work on the big-bang theory.

With the new port truss section in place, the crew is ready to move on to the second phase of the mission – rewiring the station. That work will begin Wednesday when the port solar array on truss segment P6 is folded up, allowing the P4 solar arrays delivered by the STS-115 crew to rotate and track the sun. Once that’s done, Curbeam and Fuglesang will head outside again Thursday to begin reconfiguring the external wiring so that power from the new solar arrays delivered in September can be used.

Meanwhile, after taking a close look at imagery gathered on the first three days of the flight, mission managers determined that the shuttle’s heat shield can support a safe return to Earth. They also decided a more detailed inspection that had been scheduled for tomorrow will not be necessary.

Space Shuttle Discovery’s seven astronauts woke at 9:47 a.m. this morning to the song "Waterloo" by Swedish group Abba in honor of Fuglesang, who is from Sweden. "Nice music this morning," Fuglesang said from the Quest airlock, where he spent the night preparing for the spacewalk with Curbeam.

The crew is scheduled to go to sleep at 1:17 a.m. Wednesday, after moving the space station arm into a position that will provide a good view of the P6 solar array retraction. The shuttle crew will start flight day four at 9:17 a.m. on Wednesday. The station crew will get an extra 40 minutes of sleep, awakening at 9:47 a.m.